Apparatus for driving photosensitive element in electrophotographic copier of image transfer type

ABSTRACT

An apparatus comprises a sheet of photosensitive element in the form of an endless belt, a drive roller for driving the photosensitive sheet in one direction, a suction box for sucking in a loop portion of the photosensitive sheet supported on the roller and pressure reducing means for imparting a sucking force to the suction box. The suction box regulates the direction of advance of the photosensitive sheet to prevent zigzag movement thereof and is provided with means for protecting and cleaning the photosensitive surface.

United States Patent Tanaka et al.

APPARATUS FOR DRIVING PHOTOSENSITIVE ELEMENT IN ELECTROPHOTOGRAPHIC COPIER OF IMAGE TRANSFER TYPE Inventors: Susumu Tanaka, Sakai; Yuji Enoguchi, l-ligashi-Osaka; Takao Fujiwara, Sakai, all of Japan Minolta Camera Kabushiki Kaisha, Osaka, Japan Filed: Feb. 22, 1973 Appl. N0.: 334,532

Assignee:

Foreign Application Priority Data Mar. 7, 1972 Japan 47-27584 US. Cl. 355/15, 355/16 Int. Cl G03g 15/00 Field of Search 355/3, l5, 16; 271/45,

References Cited UNITED STATES PATENTS 5/1969 Badum et a1 226/97 X 1 Feb. 25, 1975 3,495,268 2/1970 Hurst 276/97 X 3,654,901 4/1972 Donohue 355/15 3,694,068 9/1972 Jordan 355/16 X 3,723,981 3/1973 Stange 226/97 Primary Examiner-Samue1 S. Matthews Assistant Examiner-Alan Mathews Attorney, Agent, or FirmWolder & Gross [57] ABSTRACT An apparatus comprises a sheet of photosensitive element in the form of an endless belt, a drive roller for driving the photosensitive sheet in one direction, a suction box for sucking in a loop portion of the photo sensitive sheet supported on the roller and pressure reducing means for imparting a sucking force to the suction box. The suction box regulates the direction of advance of the photosensitive sheet to prevent zigzag movement thereof and is provided with means for protecting and cleaning the photosensitive surface.

6 Claims, 2 Drawing Figures APPARATUS FOR DRIVING PI-IOTOSENSITIVE ELEMENT IN ELECTROPIIOTOGRAPIIIC COPIER I OF IMAGE TRANSFER TYPE BACKGROUND OF THE INVENTION This invention relates to apparatuses for driving a photosensitive element in electrophotographic copiers of the image transfer type, more particularly to an apparatus for driving a photosensitive element in the form of an endless belt to be subjected to charging, exposure and image transfer operation for use in an electrophotographic copier of the electrostatic latent image transfer type in which an electrostatic latent image formed on the photosensitive element is transferred directly to copy paper or of the powder image transfer type in which the electrostatic latent image is developed with a toner powder to form a visual image and the visual image is subsequently transferred to copy paper.

Generally, the photosensitive sheet of the endless belt type is received around a drive roller and a tension roller and is driven under suitable tension. However, such endless photosensitive element tends to be deviated widthwise in zigzag fashion when driven and the zigzag movement becomes more pronounced if it is driven at an increased speed.

Various means for preventing zigzag travel of the endless photosensitive sheet for use with this type of driving apparatus have heretofore been proposed, but it has been extremely difficult to completely eliminate the zigzag movement inasmuch as the photosensitive sheet has to be driven in timed relation to the movement of an exposure system for the photosensitive element. If the photosensitive element is driven in zigzag fashion, it is impossible to obtain an electrostatic latent image which is an accurate copy of the original image.

The photosensitive element is used repeatedly for the production of copies. When the element undergoes fatigue and deterioration in its image bearing surface and therefore becomes no longer serviceable, there arises a need to replace the element with a fresh one, whereas if the photosensitive element is in the form of an endless belt passed around and supported on two rollers, the element is very troublesome to replace and requires complex support and drive means. The photosensitive sheet of the type described has another drawback that since it is always subjected to mechanical tension by the two rollers, the serviceable life of the element reduces.

SUMMARY OF THE INVENTION An object of this invention is to provide an apparatus for use in an electrophotographic copier of the image transfer type for driving an endless sheet of photosensitive element free from zigzag movement.

Another object of this invention is to provide a driv- 'ing apparatus of a very simplified construction which permitsan old photosensitive element to be replaced with a fresh one with extreme ease. I

Still another object of this invention is to provide a driving apparatus which is free from the necessity to mechanically give excess stress to the photosensitive element to tension the same so as to render the photosensitive element serviceable over a prolonged period of time.

According to this invention, a photosensitive sheet is supported on only one drive roller. The photosensitive sheet per se is endless or is rendered endless by being adhered to an endless support belt. The copier includes a suction box disposed in opposingrelation to the drive roller and adapted to suck in a loop portion of the endless sheet. The suction box draws in the loop portion to impart tension to the sheet and to thereby keep the sheet planar. The interior width of the suction box is nearly equal to the width of the photosensitive sheet such that the photosensitive sheet can travel along the inner wall of the suction box. The suction box is further provided on its interior wall with soft cloth such as silicone cloth or with an equivalent material so as to protect and clean the surface of the photosensitive element as it moves slidingly along the interior wall of the suction box.

According to this invention, the suction box guides the travel of the photosensitive element without permitting the zigzag movement of the element. Further this invention employs no tension roller to extremely simplify the mechanism for driving the photosensitive sheet and to mitigate troubles to be encountered in replacing the photosensitive element.

The vacuum suction to be given to the suction box varies depending upon the thickness and size of the photosensitive sheet. For copiers adapted for copy sizes generally used, a suction for example of as low as 30 mm Aq. will achieve satisfactory results. Consequently, the mechanical tension given to the photosensitive sheet is very small so that the life of the photosensitive sheet can be extended a great deal.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view in section showing the construction of principal part of an embodiment of this invention; and

FIG. 2 is a view in section showing the construction of principal part of another embodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows an embodiment of electrophotographic copier of the electrostatic latent image transfer type. A document D is placed face down on a document table 1 made of a transparent material such as glass and is illuminated by an exposure system 2. The reflected light from the surface of the document is led onto a photosensitive element P to form an image thereon for exposure, whereby the reverse of the image of the document is formed as an electrostatic latent image on the photosensitive element.

The exposure system 2 comprises first movable means including a lamp L and a reflecting mirror Ml; second movable means including reflecting mirrors M2 and M3; stationary means including an image-forming lens 3 and a reflecting mirror M4; and an exposure slit 4. As detailed in Publication of Japanese Patent Application No. 6647/1964, the first movable means travels at a velocity of v while the second movable means travels at a velocity of v12, so that in spite of the travel of both the movable means, the light path extending from the document surface to the image-forming lens 3 is maintained at a constant length all the time. For a copying operation, the first and second movable means travel reciprocally between the solid line position and the broken line position in the drawing, and the photosensitive element is exposed during the forward travel.

The photosensitive sheet P per se is endless or the sheet is rendered endless by being adhered to an endless support belt. The sheet P is passed over a drive roller 5 which is driven by rolling contact with a feed roller 6. The roller 6 is rotated by unillustrated drive means. During the advance of the first movable means of the exposure system 2, the photosensitive sheet P is driven at the same speed and in the same direction as the first movable means. To avoid damage to the photosensitive surface due to the direct contact of the feed roller 6 therewith, the roller 6 has a smaller diameter at its longitudinally central portion than at its opposite ends, which are in contact with the opposite ends of the drive roller 5 to rotate the same.

Disposed along the path of travel of the photosensitie sheet P are a charging unit 7 such as a corona discharging means for charging the photosensitive surface prior to exposure, the aforementioned exposure slit 4 for exposing the charged photosensitive surface to an image of the document and a transfer unit by which an electrostatic latent image formed on the photosensitive surface by the exposure is transferred tocopy paper 8.

The transfer unit comprises transfer rollers 9 and 10 and a transfer belt 11 reeved around the rollers 9 and 10 for bringing the copy paper 8 into intimate contact with the photosensitive surface to drive the paper at a speed equal to that of the photosensitive sheet P. Although not shown, the transfer unit is of course pro- 1 vided with known means for injecting charges into the copy paper 8 for transfer.

The copy paper 8 in the form of a roll is disposed within the machine. The leader end of the paper 8 is led between the photosensitive surface and transfer belt 11 to transfer the image. Prior to the transfer, the copy paper 8 is cut to a predetermined dimension (copy size) by a cutter 12 disposed along the feed path of the paper.

The copy paper 8 bearing the transferred electrostatic latent image thereon is separated from the photosensitive surface upon passing over the transfer roller 10 and is sent to a developing unit 13, in which a toner in the developer is applied to the latent image to visualize thesame. The paper is-then delivered onto a fixing belt 14 to fix the image by a fixing unit 15 disposed along the path of movement of the fixing belt 14. The paper is then sent out from the machine.

With the electrophotographic copier of the electrostatic latent image transfer type described, the respective operations are carried out automatically for example under programmed automatic control.

According to this invention, the copier includes a suction box 16 for sucking in a loop portion P of the endless photosensitive sheet P supported on the drive roller 5 so as to position the loop portion Palong the interior wall of the box 16 for sliding movement on the wall face when the drive roller 5 is driven.

Air is exhausted from the interior of the suction box 16 by pressure reducing means such as a simple exhaust fan 17 or the like to suck in the loopportion P. The suction box 16 is further provided on its interior wall with a soft cloth 18 such assilicone cloth or with a suitable protective sheet adhered thereto to protect the photosensitive surface from defacement. The cloth serves also as a cleaner when the photosensitive sheet P moves in sliding contact therewith.

The photosensitive sheet P is driven by the drive roller 5 in one direction at a speed equal to that of the first movable means of the exposure system 2 and subjected to charging, exposure and image transfer, upon completion of which the sheet is cleaned by the cloth. 18 or the like within the suction box. The interior width of the suction box 16 is nearly equal to the width of the sheet P and is such as to permit the sliding movement of the photosensitive sheet P, so that the pressure reducing means 17 when actuated immediately causes the loop portion P of the photosensitive sheet P to extend its photosensitive surface along the interior wall surface of the suction box 16 in contact therewith. Since a major part of the loop P of the photosensitive sheet P thus extends along the wall face of the suction box 16, with the direction of its travel very accurately regulated under suction, the remaining portion of the photosensitive element exposed from the suction box is completely prevented from zigzag movement.

The suction to be exerted by the pressure reducing means 17 within the suction box 16 may sufficiently be such that the photosensitive loop P will extend along the interior wall of the suction box. Accordingly, the acting force is small enough to render the photosensitive sheet P free of detrimental tension. The photosensitive sheet P is driven only in one direction in which the first movable means of the exposure system 2 advances. The photosensitive belt therefore circulates only in one direction for every cycle of copying operatron.

FIG. 2 is a diagram illustrating a mode of embodying this invention in an electrophotographic copier of the dry transfer type, namely of the powder image transfer type. The parts similar to those in H6. 1 are referred to by the same reference numerals.

With the electrophotographic copier of the powder image transfer type, a dry-type developing unit 20 is substituted for the developing unit of FIG. 1 (shown as a wet-type developing unit in FIG. 1). The developing unit 20 is disposed between an exposure station and transfer station to apply a toner powder to the photosensitive surface. The transfer station hasa charger 21 for transferring a visualized powder image on the photosensitive surface to copy paper 8, a guide roller 22 for guiding the photosensitive sheet P to the transfer station, and guide rollers 23 and guides 24 for guiding the copy paper 8 to the transfer station to bring the same into intimate contact with the photosensitive surface (visual powder image bearing surface) and to send the paper at the same speed and in the same direction as the photosensitive sheet P.

Upon passing through the transfer station, the copy paper 8 bearing the powder image transferred thereto is peeled off the photosensitive sheet P and fed to a fixing unit 15 for the fixing of the powder image while being transported on a fixing belt 14. The paper is then sent out from the machine.

In this embodiment, the suction box 16 must have a function to clean the remaining toner off the photosensitive surface after the completion of the image trans.- fer. For cleaning therefore, the suction box 16 is provided on its interior wall with a soft material having a high cleaning effect, such as rabbit hair 18, and a dust collector 25 is disposed behind the exhaust fan 17 to collect the toner and dust removed from the photosensitive surface.

What is claimed is:

1. In an electrophotographic copierof the image transfer type, a drive roller rotatable about a transverse axis, a suction box extending longitudinally relative to said drive roller and having in an end thereof proximate said drive roller an opening longitudinally spaced from and facing said drive roller, exhaust means communieating with said suction box at a point in said box spaced longitudinally inwardly of said end opening, and an endless belt having a photosensitive outer face and constrained to move in a path having longitudinal forward and return runs joined at opposite ends by respective first and second longitudinally spaced transverse end runs, said first transverse end run extending around said drive roller and said second transverse end run and a part of said longitudinal forward and return runs being disposed in said suction box so that the belt is tensioned under the influence of the reduced pressure therein, said suction box including opposite walls extending along the outer faces of said belt longitudinal runs and said walls having their inside faces lined with relatively soft webs engaging said belt outer faces in said suction box.

2. An image transfer type electrophotographic copier apparatus including charging, exposing and transferring stations comprising:

a drive roller;

a photosensitive element in the form of an endless belt constrained to move in a path having longitudinal runs and a first looped end adjacent to said drive roller and an opposite second looped end, said belt in said first looped end coacting with said drive roller which drives the belt;

pressure reducing means;

a suction box in covering relation to a portion of said belt including a sucking path leading to said pressure reducing means;

said belt with said driver roller at said first looped end being driven while said pressure reducing means is in operation causing said belt to rotate in the form of an endless belt without the presence of a roller at the second looped end; and

said suction box including opposite walls extending along the outer faces of said longitudinal runs of said belt path and said walls having their inside faces lined with relatively soft webs engaging said belt outer faces in said suction box.

3. An apparatus as claimed in claim 2 wherein said suction box means covers both the upper and lower surfaces of said belt except for the area where said belt traverses said charging, exposing and transferring stations 4. An apparatus as claimed in claim 2 wherein the width of said suction box covering said belt is essentially equal to the width of said belt for preventing the meandering of said belt.

5. An apparatus as claimed in claim 2 wherein said suction box is formed with a protecting means for cleaning said photosensitive element.

6. An apparatus as claimed in claim 2 including a powder collecting means discharged from said pressure 

1. In an electrophotographic copier of the image transfer type, a drive roller rotatable about a transverse axis, a suction box extending longitudinally relative to said drive roller and having in an end thereof proximate said drive roller an opening longitudinally spaced from and facing said drive roller, exhaust means communicating with said suction box at a point in said box spaced longitudinally inwardly of said end opening, and an endless belt having a photosensitive outer face and constrained to move in a path having longitudinal forward and return runs joined at opposite ends by respective first and second longitudinally spaced transverse end runs, said first transverse end run extending around said drive roller and said second transverse end run and a part of said longitudinal forward and return runs being disposed in said suction box so that the belt is tensioned under the influence of the reduced pressure therein, said suction box including opposite walls extending along the outer faces of said belt longitudinal runs and said walls having their inside faces lined with relatively soft webs engaging said belt outer faces in said suction box.
 2. An image transfer type electrophotographic copier apparatus including charging, exposing and transferring stations comprising: a drive roller; a photosensitive element in the form of an endless belt constrained To move in a path having longitudinal runs and a first looped end adjacent to said drive roller and an opposite second looped end, said belt in said first looped end coacting with said drive roller which drives the belt; pressure reducing means; a suction box in covering relation to a portion of said belt including a sucking path leading to said pressure reducing means; said belt with said driver roller at said first looped end being driven while said pressure reducing means is in operation causing said belt to rotate in the form of an endless belt without the presence of a roller at the second looped end; and said suction box including opposite walls extending along the outer faces of said longitudinal runs of said belt path and said walls having their inside faces lined with relatively soft webs engaging said belt outer faces in said suction box.
 3. An apparatus as claimed in claim 2 wherein said suction box means covers both the upper and lower surfaces of said belt except for the area where said belt traverses said charging, exposing and transferring stations.
 4. An apparatus as claimed in claim 2 wherein the width of said suction box covering said belt is essentially equal to the width of said belt for preventing the meandering of said belt.
 5. An apparatus as claimed in claim 2 wherein said suction box is formed with a protecting means for cleaning said photosensitive element.
 6. An apparatus as claimed in claim 2 including a powder collecting means discharged from said pressure reducing means. 